There have been conventionally attempts for effectively utilizing the energy generated by vibrations of a structure, such as roads, bridges, and architecture, vibrations of a moving body, such as cars, and train carriages, and vibration due to human activities. As for a method for effectively utilizing the energy generated by vibrations, there is a method where vibration energy is converted into electric energy. Examples of such a method include a system utilizing a piezoelectric element, and a system utilizing electrostatic induction.
The system utilizing the piezoelectric element uses mainly a ceramic-based piezoelectric element, and utilizes a phenomenon that electric charge is induced at a surface of the piezoelectric element when distortion is applied to the piezoelectric element due to vibrations.
The system utilizing the electrostatic induction typically uses an electret dielectric retaining electric charge semipermanently (for example, see PTL 1 to PTL 3). The electret dielectric used in the aforementioned literatures is a material capable of charging the dielectric to generate an electrostatic field semipermanently. Electric charge is induced to an electrode through electrostatic induction by changing a relative position between the electret dielectric and the electrode disposed being distant from the electret dielectric due to vibrations. As a result, electricity is generated.
Since the system utilizing the piezoelectric element uses mainly a ceramic-based piezoelectric element, there are problems that the element does not have flexibility and the element is easily broken.
In the system utilizing electrostatic induction, a charging treatment needs to be performed on a dielectrics, when an electret derivative for use is produced. Examples of the charging treatment include corona discharge, and a plasma discharge treatment. However, these treatments have a problem that a large quantity of electricity is required. Moreover, a flexibility of an element is not sufficient. In addition, a mechanical capacity varying system is typically disposed, and thus it is difficult to realize a flexible element.